I thought that too, but every time I read about someone treating their room their reactions are always like "I hear so much bass in my room that I didn't know was there now!" and what not... Why is that?
Is it because of the standing wave cancellations that are eliminated? And if so, then isn't my original statement true...? I think really it can skew your low end in either direction I guess, so bass traps affect different rooms in different ways, based on the origin of the sound and the dimension of the room...
Regardless, this summer will be bass trap building season.